If you have a SQL technical interview coming up, you already know the hard part: reading about JOINs and GROUP BY is nothing like writing them under pressure while someone watches. Flashcards and cheat sheets help you recognize syntax — they don't build the muscle memory of actually querying a database. So we built a free tool that lets you do exactly that, right in your browser.
TechLexicon's SQL Interview Warm-Up runs a real database in your browser — no signup, nothing to install, nothing sent anywhere. You type a query, hit Run, and see the actual rows come back. It's the closest thing to the real interview environment, and it's completely free.
Why we built it
This one started with a real person. Someone in an online community had a SQL technical interview in a few days for a technical-support role — and no good way to practice beyond re-reading tutorials. That's a gap we kept seeing, so we built the tool we wished existed and made it free for anyone job hunting. (It doubled as a great excuse to sharpen our own SQL, too.)
Reading SQL is recognition. Writing SQL against a live database is recall. Interviews test recall — so practice recall.
What's inside
The dataset is a realistic support/analyst setup — accounts, contacts, agents, and tickets — the kind of tables you'd actually query on the job. From there:
- A live query playground — write any SQL and run it instantly against the in-browser database.
- Level 1 — core challenges:
SELECT/WHERE, sorting and limits,COUNT+GROUP BY,INNERvsLEFT JOIN,HAVING, subqueries, and date math. - Level 2 — advanced: window functions (
ROW_NUMBER,RANK), running totals,LAG, top-N-per-group, and CTEs — the queries that separate a senior candidate from a junior one. - The "explain it out loud" questions interviewers actually ask —
WHEREvsHAVING, JOIN types, NULL handling, indexes — with clear model answers. - A pop-up cheat sheet you can pull up next to any challenge, and support-role interview tips.
One tip that matters more than any query: do a live mock interview with a real person if you can. This tool sharpens the fundamentals fast, but practicing out loud with someone is the single biggest confidence boost.
Try it before your interview
Open it on your phone or laptop, work through each challenge before revealing the solution, and you'll walk in with your SQL fresh instead of frantic. It's a preview of a full SQL practice mode coming to the TechLexicon app — but the warm-up tool is live and free right now.